Antiretroviral therapy in HIV infection preserves immune function but allows development of neurocognitive impairment (NCI) in about 50% of treated patients. We propose a new route to prevent or treat HIV-associated NCI. This application aims to test the hypothesis that induction of innate antiviral responses in monocytes can mitigate HIV infection in the brain at two levels: by preventing establishment of the HIV reservoir and by interruption of expression of neuropathogenic gene products leading to NCI. Monocytic cells are the primary target of HIV in the brain; they mediate HIV entry into the brain, but they can mount innate immune responses that block HIV infection. In vivo Type I interferon responses reduce neuropathogenesis in mice infected by chimeric HIV, EcoHIV; they restrict HIV transmission in human beings and in EcoHIV infected mice and can control SIV infection in macaques. We propose to use EcoHIV infection of conventional and various knockout mice and its induction of NCI, to define the basis of protective innate immune responses of macrophages to HIV in mice to prevent HIV infection in the brain or its associated brain disease. The Specific Aims are: 1) to test ligands to Toll-like receptors (TLR) 2, 3, 7/8, and 9 singly and in combinations for prevention of EcoHIV transit to the brain; 2) to test TLR ligands for silencing of the HIV reservoir in the brain and reversal of NCI; 3) to define key antiviral determinants of host responses during prevention or therapy of HAND by TLR ligands in an animal model by analysis of coding and regulatory RNAs and proteins using gene expression platforms, multiplex technology, bioinformatics, and fluorescence microscopy in specific cell types. Methods will include intranasal administration of TLR ligands, digital droplet PCR for sensitive measurement of viral DNA, fear conditioning assays of behavior and learning, assay of antiviral proteins in macrophages and brain by multiplex assays and microscopy, and assays of both coding and microRNA expression by NanoString technology and identification of antiviral genes or miRNA common to responses to multiple TLR ligands that prevent or control EcoHIV infection of NCI. If successful, these studies will describe novel approaches and agents for further clinical development to treat NCI in HIV infected people and to preserve brain function.